Asus allows the bus ratio used to run PC2100 on a "400" bus CPU (sys/ram of 3:4) to be used at all bus speeds, so you get "DDR354" speed using this ratio with a 133 bus (Intel's QDR533 bus). If you push that to only 150MHz CPU bus, you get a QDR600 CPU bus and a DDR 400 memory bus. Such is a relatively minor overclock for a QDR533 bus P4.
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